Why is there an extra $1 charge when purchasing the application?

For Android apps, the payments are made with credit cards in the Checkout Service of Google Play. For this, you need to register your credit card and $1 is charged to test if the registration is successfully authorized by your credit card. This amount, however, is not actually billed and is refunded not long after authorization. Please note that the additional $1 is not charged for subsequent subscription product purchases because your credit card information is already registered.